1. Field of the Invention
This invention pertains generally to model railroad locomotives. More specifically, the present invention incorporates a switch in a model railroad locomotive for selectively powering an electric motor within the locomotive using either Digital Command Control (DCC) or analog control.
2. Description of the Related Art
Model railroads have existed for many years, and have delighted many generations of people. These model railroads can be very simple, consisting of a small loop of track, a locomotive and an analog controller such as a transformer and rheostat or a variable transformer. Power is transmitted through the track from the analog controller to the locomotive. In FIG. 1, the electrical portion of a simple analog locomotive is illustrated, having power pickup through each of two rails. The power is provided directly to an electrical motor M1 and, in a slightly fancier locomotive, also to one or more lights L1. As the voltage differential between the left and right rails increases, motor M1 will be induced to rotate faster, and light L1 will burn brighter.
While this simple model railroad is adequate for some operators, a model railroad can also desirably be quite intricate and detailed, including thousands of feet of track, many locomotives, cars and cabooses, and even lights and whistles. As the model railroad gets more elaborate, it is quite common to have multiple engines operating upon the same track. Unfortunately, using the simple early controllers, it was not possible to independently control each of the engines. Instead, the track was controlled by the controller, and every engine upon the track would be operated using the same control, and would consequently operate at approximately the same speed and travel in the same direction. Whistles would sound in unison and lights illuminate in unison. Therefore, rather than controlling the trains the way a real train engineer would, a model railroad operator would instead be forced to control the track.
Further difficulties were encountered when the rheostat and power supply were not sufficiently robust to support the number of engines being operated upon the track. Prior to the implementation of electronically controlled model railroad engines, several techniques were used to provide more flexibility to the track operator. One option was to run parallel tracks, allowing several trains to run over nearly the same path, while still being separately controlled. Undesirably, this technique also required multiples of track, thereby increasing the cost in proportion to the number of independent tracks. To add a second track will, of course, double the amount of track and also double the amount of time needed to assemble the track. Furthermore, depending upon the desired track layout, there might not always be sufficient space for multiple tracks laid side by side. Finally, the aesthetic appearance of these multiple parallel tracks was in many cases unsatisfactory.
As an alternative, various sections of the track could be electrically blocked or isolated from other sections, and powered separately. Then, rather than having an entire track operating at a single speed and direction, it is possible to vary the speed of an engine from one section of track to another. Additionally, lights and whistles may be controlled independently upon these different sections of track.
Unfortunately, while the track operator has greater flexibility with this blocking technique or with multiple tracks, the operator is still controlling the track and not the train. Furthermore, the behavior of these analog controllers does not fully reflect the behavior of an actual train. Model trains using electric motors tend to come up to speed quite rapidly, and will tend to lurch when the applied power varies suddenly. In contrast, a real train has unique motion or acceleration characteristics that describe how fast it speeds up and slows down. The acceleration characteristics of a real train are determined by the weight of the train, the available torque within the locomotive, the terrain being traveled, and whether the locomotive is operating individually or as part of a multiple unit lash-up.
More recently, with the advent of more capable and complex electronic circuitry, electronic motor controllers have been developed that allow track operators to become model railroad engineers, controlling the speed and direction of each train independently of other trains upon a track, rather than controlling the track. These newer electronic control systems are commonly referred to as Digital Command Control (DCC), where a digital control signal is passed to a decoder. For the purposes of this disclosure, a decoder will be defined herein to be an electronic circuit which, when installed in a locomotive or similar machine, receives digital packets of information from a command station and either supplies power to the locomotive motor or controls features on the locomotive such as lights, sound or other auxiliary devices. These control signals may be used by the decoder to effect both speed and direction control of the engine relatively independently of the magnitude and polarity of the decoder electrical energy input. When the motor is powered through the decoder, digital code words are used to uniquely identify each train upon a track. The unique code word is sent out together with control instructions, and only the unique decoder addressed by the code word will process those particular control instructions. In this way, multiple trains may each be controlled independently on a single track. A block diagram of a DCC type decoder is illustrated in FIG. 2. Power is provided from left and right rail pickups, and passes through a decoder for regulation and delivery to motor M1 and one or more lights or whistles L1.
Several patents are exemplary of the use of a DCC, including Hanschke et al in U.S. Pat. No. 4,572,996 and Rossler in U.S. Pat. No. 2,571,723, each which are incorporated herein by reference for their teachings of DCC systems. In Hanschke et al, an electronic circuit monitors the voltage across a track for pulses. When pulses are detected, the digital code present within the pulses is analyzed for instructions regarding speed. When pulses are not detected, and after passing through a bridge rectifier and Darlington transistor, the track power is applied to the motor. However, until a track voltage great enough to energize the electronic circuit is reached, the Darlington transistors will not be energized, and the train will not operate. Furthermore, even when operational, there will still be an equivalent of approximately four diode voltage drops, two across the bridge rectifier and an equivalent of two more through a Darlington transistor. This voltage drop will amount to approximately three volts, which is a substantial voltage differential between the Hanschke et al vehicle and an analog train. Consequently, the Hanschke et al patent operates as illustrated in prior art FIG. 2 illustrated herein, which requires power from the rails to pass through a decoder before being provided to motor M1. In Rossler, a plurality of motors are provided which may be separately controlled through the decoder, to effect movement of the locomotive. The concept of uniquely addressing different locomotives is also discussed, as are a number of other DCC concepts. Nevertheless, like Hanschke et al, the decoder of Rossler intervenes between power at the rails and the motor.
Unfortunately then, prior art DCC decoders require sufficient voltage to operate the electronic circuitry before the motor will be powered, just as illustrated in the Hanschke et al and Rossler patents. The motor must be powered before the engine can begin to move the train, and the voltage required to operate electronic circuitry is greater than that normally required to start an analog engine. Unfortunately, this also means that an analog engine will attempt to drive the train prior to the DCC engine being powered. The resultant mechanical load on the analog train motor may be too great, particularly with a relatively low starting voltage and the resultant low starting torque. Should the load be too great, the motor may draw too much current and overheat or otherwise be damaged, or potentially cause damage to other parts of the system. Consequently, it has not been possible in the prior art to lash together analog trains taking power directly from the track with trains that first condition the power through a decoder. Where an analog track is used to power separate analog and DCC locomotives, and where the voltage applied is relatively low, there will also be an undesirable and significant speed difference between the analog and DCC locomotives.
Efforts have been made in the prior art to condition a digital signal to allow it to power analog trains as well as DCC trains. This may be accomplished by forming a control signal which will activate a DCC train, and which will also provide an RMS voltage appropriate for an intended analog drive. A patent exemplary of this technique is U.S. Pat. No. 5,749,547 to Young et al, the contents of which is also incorporated herein by reference. In Young et al, a digital signal may be provided through various techniques, including DC offsets superimposed onto an AC signal, or through various transmission techniques including RF transmission and frequency shift keying (FSK). Nevertheless, this technique disclosed by Young et al still requires voltages high enough to enable the electronic circuit before energizing the motor, and further requires relatively complex and expensive hardware and software to implement. As might be appreciated, this method requires complex circuitry to generate the DCC signals, and only applies to tracks that include this type of controller. Furthermore, the variations amongst electrical motors are great enough that not all analog locomotives can be powered this way without damage. What is desired then is a way to selectively control a model railroad locomotive with either DCC or analog control, thereby allowing an analog train locomotive and a train locomotive controlled by the present invention to be ganged together into a single train on the track, without risking damage to either locomotive.